mus: Embedder can request and observe BeginFrame for embedded client.

ui/aura/window_port.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_AURA_WINDOW_PORT_H_
 #define UI_AURA_WINDOW_PORT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 65 matching lines @@
                                  int64_t old_value,
                                  std::unique_ptr<ui::PropertyData> data) = 0;
 
   // Called for creating a cc::CompositorFrameSink for the window.
   virtual std::unique_ptr<cc::CompositorFrameSink>
   CreateCompositorFrameSink() = 0;
 
   // Get the current cc::SurfaceId.
   virtual cc::SurfaceId GetSurfaceId() const = 0;
 
+  // Requests to be notified (via |callback|) when the client app embedded
+  // inside this window receives a BeginFrame.
+  virtual void SetNeedsBeginFrames(bool needs,
+                                   base::RepeatingClosure callback) = 0;
+
   virtual void OnWindowAddedToRootWindow() = 0;
   virtual void OnWillRemoveWindowFromRootWindow() = 0;
 
  protected:
   // Returns the WindowPort associated with a Window.
   static WindowPort* Get(Window* window);
 
   // Returns the ObserverList of a Window.
   static base::ObserverList<WindowObserver, true>* GetObservers(Window* window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_PORT_H_